LEDs have been used for decades in applications requiring relatively low-energy indicator lamps, numerical readouts, and the like. In recent years, the brightness and power of individual LEDs have increased substantially, resulting in the availability of devices capable of high power output.
While small, LEDs exhibit a high efficacy and life expectancy compared to traditional lighting products. A typical incandescent bulb has an efficacy of 10 to 12 lumens per watt and lasts for about 1,000 to 2,000 hours; a typical fluorescent bulb has an efficacy of 40 to 80 lumens per watt and lasts for 10,000 to 20,000 hours; a typical halogen bulb has an efficacy of 15 lumens per watt and lasts for 2,000 to 3,000 hours. In contrast, today's white LEDs can emit more than 140 lumens per watt with a life expectancy of about 100,000 hours.
Thus, LED lights are efficient, long-lasting, cost-effective, and environmentally friendly. For the above reasons, LED lighting is rapidly becoming the light source of choice in many applications. Significant interest exists in replacing lighting products currently in use, such as incandescent and compact fluorescent (CFL) bulbs, with a corresponding LED lamp that has the same form, fit, and function. For a particular lighting fixture that uses an A19 bulb, it is desirable to “swap out” a 60 W incandescent bulb with an LED lamp that emits approximately the same amount of light but has a much longer life expectancy and reduced operating cost.
The term “Energy Star” refers to the U.S. government's energy performance rating system program that is jointly managed by the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA). According to Energy Star guidelines, a 40 W incandescent bulb nominally emits 450 lumens, while a 60 W incandescent bulb nominally emits 800 lumens. Thus, to be considered a valid replacement for a 60 W incandescent bulb, an LED lamp should emit at least 800 lumens.
LED lamp manufacturers strive to improve LED lamps. Some important ways that manufacturers can improve LED lamps is in LED emitter luminous efficacy, AC to DC power supply conversion efficiency, power factor, optics, and thermal management. Luminous efficacy is a measure of how well an LED emitter produces visible light, i.e., the ratio of visible light produced to power consumed by the LED emitter. LED lamp manufacturers want to produce LED lamps which generate more light for the same amount of energy consumed, or consume less energy yet generate the same light output. The efficiency of LED lamps can be improved by utilizing LED emitters which consume less energy when generating light, or power conversion efficiency can be improved by reducing the amount of energy consumed by control logic in the LED lamp's power supply. As lower power consumption LEDs are developed, control logic consumes a higher percentage of the total power of an LED lamp, and reducing the power consumption of the control logic has a greater effect on total efficacy.
Power factor is the ratio of real power consumed by an LED lamp and the apparent power flowing through the LED lamp's circuits. A power factor of 1 is ideal, and indicates that AC power is being utilized by an electronic circuit during the entire period of the AC sine wave, i.e. 0 to 360 degrees. With a power factor of 1, all power flowing to the LED lamp is being consumed by the LED lamp. The power factor can be lowered when the LED lamp is consuming energy for only a portion of the AC phase, or when the LED lamp is consuming power out of phase with the alternating current (AC) power source. A low power factor indicates that more current is being transmitted to the LED lamp than is actually needed to power the LED lamp. A low power factor results in unbalanced loading in the power transmission and distribution lines, and unnecessary power loss.